When Nicholas Nixon was visiting his wife’s family in the summer of 1975, he asked all four sisters – left to right: Heather, Mimi, BeBe, and Laurie – to pose for a photo with each other.

The very next year, at one of the sisters’ graduation, he asked for another photo in the same order.

Year after year Nixon has taken snapshots of the siblings to document their growing up and aging together.

These photos were exhibited at the Museum of Modern Art in New York City in a a collection that went along with the publication of the museum’s book, The Brown Sisters: Forty Years, that documented their lives.